Rubber compounds constituting rubber members for tires, for example vulcanized rubber compounds used inside a tire such as a bead apex, is required to have high rigidity in order to improve the steering stability.
For the purpose of increasing rigidity of vulcanized rubber compounds, there have been proposed adding a large amount of filler, adding a thermosetting resin (patent document 1), adding fibrous fillers (patent document 2), blending butadiene rubber comprising 1, 2-syndiotactic polybutadiene crystals (sPB) (patent document 3).
However, the above listed methods tend to deteriorate the low fuel consumption property which is an important performance requirement.
For example, a rubber compound having a complex elastic modulus higher than 90 MPa, significantly deteriorates the low fuel consumption properties, therefore, it is difficult to use it for a tire practically.
In view of the above, the inventors of the present invention have conducted various researches. As a result, the inventors of the present invention have succeeded in providing a rubber compound capable of satisfying both high elasticity and low fuel consumption property in a range previously not reached by improving combination of materials composing the rubber compound which have been individually known (hereafter, may be referred to as “compounding tuning”).